Slurs

[Antoniouk Sergio]

Thanks to everybody who helped me - lilypond now works very well, but
I got next problem:

I try to typeset some piece of music with two voices. I do it like
this

\score
{
  \notes \context Staff = "StaffA" {
      \relative c''
      {
       a' g f e | d8 f e g 
       <
         \context Voice = "VS" { \stemUp f4. d8 }
         \context Voice = "VA" { \stemDown a8 c b d }
       > |
      }
   }
}

Everything looks good, but I need two slurs - one from a' in first
bar to f4. in voice VS, and second slur from g in second bar to f4.
in voice VS. 
When I try to do it like this

\score
{
  \notes \context Staff = "StaffA" {
      \relative c''
      {
       a' ( g f e | d8 f e g (
       <
         \context Voice = "VS" { \stemUp ) ) f4. d8 }
         \context Voice = "VA" { \stemDown a8 c b d }
       > |
      }
   }
}

I got some error message similar to "unclosed slur", and
no slurs appeared in output.

Can you help me please?